Be strong. Dance seems effortless to the audience. That's because it's a dancer's job to make it look effortless; they get paid to make it look easy. In reality, dance is an intense cardio and core strength workout. Practicing yoga and Pilates are two great methods of building stamina and strength without creating body-builder bulk.
Gain flexibility to compliment your growing strength. You'll need exceptional flexibility in the hamstrings, hips and back in order to achieve that magnificent extension the stars have. Check out the links below for help with gaining greater flexibility.
Find a dancing school that caters to your needs. If you're 30 years old and want to learn to tap dance, make sure you find a school that has tap classes for adults. If you're 14 and have a passion for contemporary dance, seek out a studio that specializes in modern dance for teenagers.
Don't turn your nose up at ballet. Even if you don't aim to be a prima ballerina, ballet is the foundation of most types of western dance. Learning ballet fundamentals and terminology will help you enormously in your dance journey.
Practice, practice, practice. Learning choreography is a challenge of the mind. While your body is performing the movements, your brain has to constantly be eight beats ahead, reminding you where to go next and how to recover in case you goof up.